Human skin contains a number of appendages. Vascular and lymphatic channels provide for nutrition, healing and transport. Sweat and sebaceous glands provide respectively for thermal control and lubrication. Pigmented structures provide for sun protection. Hair follicles and individual hairs provide for insulation, protection and individual differentiation.
Growth of each hair is originated by germinative fibroblast cells in the basal layer of the epidermis. The hair grows both outwards and inwards during its growth cycle, and the follicle develops as an encapsulating pouch extending beyond the epidermis and down several millimeters in depth to the subcutaneous fat. Hair remains attached to the base of the follicle, where a capillary network develops to provide nourishment. During the anagenic growth phase, hair matrix cells divide rapidly and migrate upwards to form the shaft. A subsequent catagenic phase is marked by cessation of mitosis, and the reabsorption of the lower part of the follicle. Capillary nourishment is greatly reduced during this phase. In this or the final telogenic (resting) phase, the hair falls out and a new hair may replace it in a new growth cycle. At any particular time, approximately 10% of scalp hairs will be in telogenic mode.
The growth cycle varies with anatomical location from as little as 3 months for facial hair to as much as 7 years on the scalp. Hair in high friction pubic areas may be retained by the body as protection and may not shed at all.
The hair follicle consists of a mixture of germinative cells and melanocytes. Sebaceous cells empty into the follicle, providing a lipid-rich environment. The follicle is typically 0.1 mm in diameter and may extend to 4 mm in depth. The average hair diameter within the follicle is 60 um. Hair itself is generated as an accumulation of dead (keratinized) cells. Structurally it consists of two or three discrete layers, as shown in FIG. 1. The outer cuticle layer consists of a single layer of overlapping flat cells like the scales of a fish. This acts as a protective barrier. An inner cortex layer contains any pigment which may be present (pigment may also reside in melanocytes lining the follicle). Pigment may exist as two melanin forms. Eumelanin is responsible for brown/black coloration and pheomelanin is responsible for red/blonde coloration. Larger, fully developed terminal hairs also contain a core known as the medulla.
In the lower follicular region, a bulge is formed where the arrector pili muscle contacts the follicle. This muscle controls movement and orientation of the hair and may, under appropriate stimuli, render the hair vertical with respect to the skin surface. The bulge area has one of the fastest rates of cell division found in mammals, stimulated by growth factors from the lower papilla area.
While the hair follicle and hair contained therein function at several different levels, excess body hair does present a cosmetic problem for hirsute females. As a consequence, many individuals undergo hair removal treatments. Conventional techniques, including electrolysis, shaving, wax epilation and tweezing, are often painful and temporary.
Electrolysis is used by an estimated 1 million women in the United States. Two techniques dominate the electrolysis field. Galvanic (DC) current can be passed down a fine needle inserted into the follicle. This converts tissue saline locally to sodium hydroxide, which destroys the follicle. Alternatively, the thermolysis technique utilizes an AC current to directly heat and thereby destroy the papilla. Some clinicians utilize a combination approach of these two electrolysis techniques. All electrolysis methods treat a single follicle at any time, in a painful procedure which can require analgesia. Disposable needles are used in this non-permanent, time consuming, multiple treatment technique.
Several contemporary photonics techniques have been evaluated.
In 1993, Thermotrex Corporation was assigned two Hair Removal Device and Method patents (U.S. Pat. Nos. 5,226,907 and 5,425,728) based on the use of an externally applied chromophore to enhance local absorption of laser light. In these patents, a topically applied substance is said to penetrate to the full depth of the root of the follicle. The substances cited include permanent hair dyes, suspensions of carbon particles and photosensitizing compounds. A subsequent application of laser light is said to induce a photothermal reaction which destroys the follicle and a surrounding tissue area.
The compounds cited by Thermolase in their patents will probably demonstrate follicular selectivity. Many other topical compounds, and some systemic compounds, exist as candidates. Liposomal or lipophilic compounds may favor the lipid rich environment. Alternatively, solvents such as ethanol may be used to de-lipidize or re-organize the sebum, and thereby open the follicular passageways. Deposition of hydrophilic drugs may be facilitated by the action of wetting agents such as sodium lauryl sulfate, which may promote the creation of an emulsion. Particle size clearly plays a role in terms of ability to penetrate through narrow epidermal structures and along the follicular duct. The approach cited in this invention may work, although its practice involves the use of expensive laser equipment. Further, the use of topical compounds prolongs treatment and raises potential risk.
A second technique has been studied and reported by Drs. Melanie Grossman and Rox Anderson whereby single high energy normal mode Ruby laser pulses are applied to the skin in the absence of an externally applied chromophore. No issued patent has been awarded covering this work. In this method, the optical target is the melanin within the inner cortex layer and the pigment-bearing melanocytes lining the follicle. High fluences of up to 60 J/sq.cm. are utilized in large spotsizes, with short pulsewidths of the order of 150 .mu.sec and a wavelength of 694 nm. This technique employs a number of natural phenomena to enhance effect on the deep follicular component. A large applied spotsize and high fluence allow for maximum depth of penetration. Concurrent cooling spares bulk tissue structures from the edema and general damage which can result from the use of fluences of this magnitude. Intimate index-matched contact of the custom handpiece with the tissue minimizes reflection loss. However, the short pulsewidths used in this approach are unlikely to efficiently transfer heat to the entire follicular structure. The Ruby laser is not readily capable of the requisite millisecond-domain pulses necessary to effect a true thermal mechanism.
A third approach, utilizing the Q-Switched Ruby laser, was disclosed by Nardo Zaias in his 1990 U.S. Pat. No. 5,059,192. This patent cited the use of a Q-Switched Ruby laser at 694 nm, with 3-8 mm spotsize and around 8 J/sq.cm. Pulsewidth was in the range 30-40 nanoseconds. Light energy administered in such a short pulsewidth will be well retained in the melanocytes lining the follicle. This approach will provide potential for melanocyte destruction and perhaps permanent depigmentation or destruction of the hair, but likely will not kill the follicle itself, since the pulsewidth is insufficiently long to conduct heat away from the targeted melanin granules.
Other approaches have been described.
In 1967, U.S. Pat. No. 3,538,919 was filed by R. Meyer. Meyer cited the placement of a fiber directly into the follicle into which a total of 30-40 J/cm.sup.2 of light was subsequently launched. This fluence was administered over a period of 1-2 milliseconds, preferably by a normal mode Ruby or Nd:YAG laser. Use of a 50 um fiber was cited. This fiber diameter would theoretically fit into a 100 um follicle containing a 50 um hair, but with some difficulty. Also, the technique would be time consuming to administer, on a single hair-by-hair process.
In 1970, Richard Harte filed U.S. Pat. No. 3,693,623, which also cited the placement of a fiber directly into each follicle to be destroyed. The light source here was a xenon lamp, which applied up to 3 mJ to each follicle, in an interval of less than 3 msec. This technique again addresses each hair individually in a tedious and difficult to administer process.
In 1973, Carol Block filed U.S. Pat. No. 3,834,391, which similarly addressed the placement of a fiber at the follicular entrance. Light source was unspecified. This patent introduced the concept of the use of mineral oil, said to facilitate light conduction, presumably by index matching. No additional chromophore was added. This technique in this patent calls for the destruction of each hair on an individual basis in a tedious and difficult to administer process.
In 1981, H. Weissman filed a patent, later granted as U.S. Pat. No. 4,388,924. This cited the devitalization of hair by the specific destruction of the papillary blood supply. A narrow beam from an Argon laser was directed onto the tissue. This light was said to be absorbed by the papillary plexus, causing heating and coagulation. Multiple 20-30 millisecond exposures from a 0.5-2.5 Watt beam were cited. The hair was subsequent tweezed from its follicle. This method suffers again from the individual hair-by-hair approach, which is time consuming. Also, the selective destruction of the papillary plexus is unlikely to be practical using a narrow beam Argon laser, with its limited penetration depth capabilities, since this supply resides at several millimeter depth and is shielded by the overlying follicular structure. Indeed, no vascular specific lasers are likely to exhibit adequate dermal penetration.
In 1984, A. Sutton filed a patent, later granted as U.S. Pat. No. 4,617,926. This provided for the use of a fiber without a core, into which an individual hair slides by 2-3 mm, completing the waveguiding action. Different probes were cited, and about 1 Joule of energy launched into the fiber, from an unspecified laser source. In an alternative embodiment, the fiber is sharpened and inserted directly into the follicle. This technique is time consuming and tedious and is likely to result in rapid probe destruction.